1. Field of the Invention
The present invention relates to thermal-based memory technology, such as phase change material memory technology.
2. Description of Related Art
Phase change memory is a class of non-volatile memory integrated circuit technology that is thermally-based. A phase change memory cell may be comprised of top and bottom electrodes, and a layer of phase change material in between the electrodes. The phase change material has at least two solid phases, including for example a generally amorphous solid phase and a generally crystalline solid phase. The phase change material can change phase by application of electrical current through the layer of phase change material. The generally amorphous state is characterized by higher resistivity than the generally crystalline state. The differences in resistivity can readily be sensed to detect data stored by the phase change memory cell.
The change from the amorphous to the crystalline phase, referred to herein as the SET operation, may be performed by applying an electrical pulse through the phase change material. In the electrical pulse, an initial peak current is followed by decreasing current over the duration of the pulse so that the phase change material slowly cools into the crystalline state.
The change from the crystalline phase to the amorphous phase, referred to herein as the RESET operation, may be performed by applying a short high current pulse through the phase change material to melt or break down the crystalline phase structure in the phase change material. Afterwards the phase change material cools quickly, quenching the phase change process and allowing at least a portion of the phase change material to stabilize in the amorphous state.
Phase change memory has the advantageous properties of scalability, DRAM-like operation and non-volatility, which make it a good candidate for storage class memory. However, SET/RESET cycling of a memory cell causes stress which over time causes degradation of the phase change material in the memory cell. This degradation of the phase change material in a memory cell is associated with endurance issues including cells no longer being able to store data. Proposed solutions to improve the endurance of phase change memory have been based on various material and structural innovations, such as material doping, confined cell structure, and operation optimization. However, these proposed solutions do not address degradation of the phase change material which will limit the endurance of the phase change memory.
It is therefore desirable to provide devices supporting a method of increasing the endurance of phase change memory cells by reducing degradation of phase change material in the memory cell.